1. Field of the Invention
The present invention relates to an electrically driven grinder for ceramic cutlery adapted to sharpen an edge of the ceramic cutlery by bringing the edge thereof orderly into sliding contact with a diamond abrasive wheel for rough machining and a diamond abrasive wheel for finishing machining which are rotated at a high speed.
2. Prior Art
Recently, since cutlery has been required to have good abrasion resistance, chemical and corrosion resistance, ornamentalness, generally ceramic cutlery starts to be used in most households instead of a metal cutlery. But, since the ceramic cutlery has a very hard blade provided with a specialized edge shape, the edge is apt to suffer from being wasted away and/or chipped away to loose its sharpness. Even if the edge of the cutlery looses its sharpness due to those causes, a whetstone or an abrasive wheel which has been used conveniently generally among the households up to this time for sharpening metallic cutlery is not useful for sharpening the ceramic cutlery.
When studying that reason, as disclosed in Japanese Patent Publication No. 62-181860, in order to prevent the edge breakage of the ceramic cutlery and to maintain the edge sharpness thereof, it is necessary to configure the edge of the ceramic cutlery in a two stepped manner to have a tapered thick portion and an edged sharp portion formed continuously thereto, but an edge angle of which is larger than that of the metal cutlery. In practice, the metal cutlery has its edge angle often formed at an acute angle between 2 degrees and 3 degrees depending on its use. To the contrary, the ceramic cutlery has its edge angle formed in a range of 10 degrees to 45 degrees because it is apt to chip away in comparison with the metal cutlery.
On the other hand, as shown in FIG. 5, a conventional cutlery grinder 41 for sharpening an edge of metal cutlery comprises a diamond abrasive wheel 42 rotatably arranged within a casing 48 and having a grinding surface 44 for rough machining and a grinding surface 46 for finishing machining. The diamond abrasive wheel 42 comprises a substantially disc-shaped member 47 formed by connecting two truncated cones 43, 45 to each other so as to have a substantially V-shaped groove formed in its periphery by their tapered surfaces with different inclination angles. The grinding surfaces 44, 46 are provided by securing different sizes of diamond abrasive grains onto the tapered surfaces by means of electrode position or the likes. When being sharpened, the edge of the metal cutlery is directed to the grinding surfaces 44, 46 by a guide slot 50 formed in a cover member 49 disposed to cover the casing 48 while the guide slot 50 intersecting with an axis of the diamond abrasive wheel 42. Incidentally, in this diamond abrasive wheel 42, an angle xcex3 defined by the rough grinding surface 44 and a plane orthogonal to the axis thereof is set to 20 to 25 degrees, and an angle xcex8 defined by the finishing grinding surface 46 and a plane orthogonal to the axis thereof is set to 26 to 30 degrees (refer to Japanese Patent Post-Examination Publication No. 6-61686).
When sharpening the edge of the metal cutlery by this cutlery grinder 41, the edge of the metal cutlery is brought into contact with the grinding surfaces 44, 46 of the diamond abrasive wheel 42 and then moved forward and backward reciprocatively through a haft thereof held by a hand. Thereby, the diamond abrasive wheel 42 is rotated, so that the edge of the metal cutlery slides relatively on the grinding surfaces 44, 46 to be sharpened.
In this cutlery grinder 41, however, since the diamond abrasive wheel 42 is rotated by its sliding resistance relative to the cutlery, its rotational speed is slow. Therefore, even though this cutlery grinder 41 is used for sharpening hard ceramic cutlery, it is impossible to sharpen it. In addition, since this grinder 41 is inherently designed for the metal cutlery, inclination angles of the grinding surfaces 44, 46 formed in the diamond abrasive wheel 42 are too large to obtain an adequate edge angle required for the ceramic cutlery.
Accordingly, when sharpening the ceramic cutlery, since the cutlery must be sent back to its manufacturer for edging it. Thus, there is such a problem that a user can not utilize the cutlery all the while and further the edge sharpening costs the user. Further more, when a ceramic knife 60 is sharpened in its manufacturer, as shown in FIG. 6, an expert must hold a haft 62 of the ceramic knife 60 and press an edge 61 onto a revolving grinding surface 52 of the diamond abrasive wheel 51 so as to obtain the adequate edge angle required for the ceramic knife 60 with skillfulness. Therefore, it is impossible for ordinary people to sharpen the ceramic cutlery in that way.
It is an object of the present invention to provide an electrically driven grinder for ceramic cutlery which is capable of sharpening an edge of ceramic cutlery readily at a predetermined edge angle by an ordinary people except an expert.
The present invention is directed to solving the aforementioned problem and resides in an electrically driven grinder for ceramic cutlery, having: a diamond abrasive wheel for rough machining comprising a disc-shaped member provided with a grinding surface on its periphery;: a diamond abrasive wheel for finishing machining comprising a substantially disc-shaped member provided with grinding, surfaces forming a V-shaped groove on its periphery, both diamond abrasive wheels being attached onto a rotary shaft coupled to a driving source; and a cover member provided with guide slots for directing an edge of ceramic cutlery to the grinding surfaces of the respective diamond abrasive wheels, an angle defined between the grinding surfaces forming the V-shaped groove of the diamond abrasive wheel for finishing machining and a plane orthogonal to the rotary shaft being set to 10 to 20 degrees, and an angle defined between the guide slots of the cover member and a plane orthogonal to the rotary shaft being set to an angle of 12 to 18 degrees.
The electrically driven grinder of the present invention allows the formation of an edge having an edge angle of 35 to 45 degrees in the ceramic cutlery, therefore, obtaining high sharpness without any chipped portions by. grinding the edge of the ceramic cutlery with this grinder.
Further, in the present invention the sizes of diamond abrasive grains may be set to #600 to #1000 in grain size number on the grinding surface of the diamond abrasive wheel for finishing machining, and the sizes of diamond abrasive grains on the grinding surface of the diamond abrasive wheel for rough machining may be set to #150 to #350. Accordingly, the edge of the ceramic cutlery can be sharpened in a comparatively short time as well as a sharp cutting capability can be recovered.